About every 3rd 4rth time I do a cold boot, my graphics card simply doesn't start. The computer boots up into windows 7 fine, but the display is completely dead. I have my power button configured in Win 7 to execute "shutdown". So after waiting for a few min for windows to load with a dead display, I simply shutdown using the power button and then power on again and everything is fine. It never happens twice in a row. Has anyone else had these issues with AMD cards?

I have crossfired dual HD4850s and an Asus X48 motherboard. I did install a 3rd party bios (from a manufacturer other than that of my Visiontek radeons) so I'm wondering if this has something to do with it - but I can't remember if this ever happened with the original bios.